As is well known in this art, HPS lamps, generally speaking, are difficult to start and require special circuitry for restarting if the lamp is extinguished after sufficient operation to elevate its temperature. This is normally referred to as hot restarting and is known to require high voltage across the lamp, considerably higher than the line operating voltage.
Numerous circuits have been developed for the purpose of hot restarting such lamps, as well as starting and operating circuits, and many of those circuits operate quite satisfactorily. However, the operative circuits which are commonly used include numerous resistors and/or pulse transformers, apart from the conventional ballast, to accomplish the starting operation. The resistors, which are commonly low resistance but have high wattage ratings, generates significant heat, necessitating special designs to either extract the heat or package the circuit in such a way that the heat does not damage other components. In addition to the heat generation, the resistive losses are wasteful of energy and the use of the resistors as well as pulse transformers increase the cost of the circuits.